The default parameters for amount and threshold are 1.0 and 0.05. I will add an overload that only needs two parameters the next release. You can compare the images with the Compare method to get the difference:
Why are you using the Unsharpmask method? What are you trying to accomplish?
using (MagickImage image = new MagickImage("logo:")) { image.Unsharpmask(0, 5, 1.0, 0.05); // Next release// image.Unsharpmask(0, 5); // Save to file so you can see the result image.Write(@"C:\logo.png"); using (MagickImage other = new MagickImage("logo:")) { MagickErrorInfo info = image.Compare(other); Console.WriteLine(info.MeanErrorPerPixel); } }